In order to reduce the negative effect of salinity on fruit yield, 5-day-old tomato seedlings (Lycopersicon esculentum) were haloconditioned by complete immersion in osmotic/saline solutions composed of PEG (−0.5, −0.75, −1 MPa), with or without 10 mM NaCl, for 1, 3, 5 and 8 days. Under moderate salinity (7.5 dS m−1), the pre-adapted plants produced 23% more shoot biomass and fruit yield than the non-adapted plants. In addition to the induced vigour, the improved tolerance in most pre-treatments was related to lower Na+ and Cl− concentrations in the leaves and increases in leaf K+ contents and K+/Na+ ratio, but the contrary was also observed. Overall, the most effective haloconditioning treatment seems to be the application of −0.75 MPa for 3 days. During the experiment in greenhouse, some vigorous haloconditioned plants were propagated through adventitious apex culture and evaluated under salinity in a short-term experiment. The results suggested that the induced salt tolerance was not horizontally transmitted, indicating that (i) the individuals chosen were not genetically more vigorous, but (ii) it is likely that they responded better to the induced adaptation, and (iii) this adaptation is probably mediated by epigenetic changes taking place in the roots.

The authors are grateful to the Spanish Ministerio de Ciencia y Tecnología and CSIC for a grant to M. Parra and to A. Albacete, respectively. Research supported by the Fundación Séneca (Comunidad Autónoma de Murcia, Spain) (project PI-58/0816/FS/01) and by the UE project IC-CT98-031.

The authors dedicate this paper to the memory of the late Professors Manuel Caro (CEBAS-CSIC) and Gilles Guerrier (Université d’Orléans, France).

Peer reviewed